Let
me propose a thought experiment. Imagine, if you will, that there's a certain
clump of nerve cells in the brain that's essential for conscious awareness. Now
suppose that a certain drug suppresses neural activity in just this nucleus,
with no effect on the rest of the brain. Subjects who take this drug do things
as usual, but they experience nothing. The drug converts them into sleepwalkers.
Finally, imagine that I've developed a new form of this drug, which has permanent
effects. It abolishes consciousness forever, with no effect on behavior. I want
to test it on you. How much will you charge to take it?

I think the question answers itself. Spending your life as a sleepwalker is
equivalent to being dead, and so you will charge me whatever price you would
charge to commit suicide.

I offer this thought experiment to dispel the notion that conscious awareness
is too metaphysical and subjective a phenomenon for science to concern itself
with. The phenomenon of consciousness is the source of all value in our lives.
As such, it should be at the top of the scientific agenda. Yet despite its
fundamental importance, consciousness is a subject that most scientists are
reluctant to deal with. We know practically nothing about either its mechanisms
or its evolution. In fact, many distinguished scientists and philosophers
believe that consciousness has no evolutionary history, because they think that
human beings are the only creatures that have it. Although most scientists will
admit in private that our close animal relatives probably have mental lives
something like ours (because, after all, they have bodies and brains and
behavior that resemble ours), a lot of scientists are reluctant to say so
plainly and publicly; and those who do can count on being accused of
sentimentality and anthropomorphism.

If you have a dog, you have probably had the experience of seeing your dog
search out a favorite toy and bring it to you in hopes of getting you to play
with him. It's hard even to describe these familiar experiences without saying
things like, "The dog was trying to find his ball," or "The dog
wanted me to play with him." But scientists aren't supposed to say things
like that, at least when we have our lab coats on. If we discuss such things at
all, we prefer to do so in some way that doesn't involve attributing intentions
or any other mental states to the dog.

There are at least two ways we can do this. First, we can use clumsy
behavioral circumlocutions for mental language. Instead of saying, "The dog
looked for his ball until he found it," we can say something like,
"The dog exhibited repeated bouts of investigative behavior, which ceased
after he contacted the ball." This somehow manages to suggest that the dog
wasn't thinking about the ball while he was looking for it, and that he didn't
perceive anything when he got it in his mouth.

Second, if we find these circumlocutions silly and tedious, we can adopt some
variant of what is sometimes called "logical behaviorism," in which
the mental words are still used but they are redefined in terms of the
probabilities of certain behaviors. In this view, a dog's intentions and desires
and beliefs turn out, when properly understood, not to be something inside the
dog, but theoretical constructs pinned on the dog by a human observer.
Therefore, the human observer can know whether the dog has intentions and
desires and beliefs, but the dog can't.

Why Not Attribute Consciousness to Animals?

Why do scientists and philosophers go through all these contortions to avoid
attributing mental states to animals? There are several reasons, some of which
are better than others. There's no doubt that sentimentality and uncritical
anthropomorphism are real temptations, and that they should be avoided in
describing and analyzing the behavior of nonhuman organisms. A lot of us succumb
to these temptations. We all know people who insist on telling you what kind of
music their begonia likes or what their cat thinks about Rush Limbaugh. These
people are mistaken. And scientists sometimes make similar mistakes. Some of the
early Darwinians in particular were guilty of this sort of thing. Because
Darwin's opponents often cited the mental and moral differences between people
and beasts as reasons for rejecting the whole idea of evolution, many of his
early followers tried to play down those differences by repeating anecdotes they
had heard about the nobility of dogs and the self-sacrifice of chickens.

The British psychologist C. Lloyd Morgan was dismayed by this uncritical
attribution of human mental states to animals, and he tried to put a stop to it.
In 1894, Morgan laid down the following law:

In no case may we interpret an action as the outcome of the exercise of a
higher psychical faculty, if it can be interpreted as the outcome of the
exercise of one which stands lower in the psychological scale.

"Higher" here turns out to mean
"humanlike," as it often did in the nineteenth century. Successive
generations of experimental psychologists have adopted this dictum as a
fundamental axiom called Morgan's Canon. It's generally thought of as a special
case of Occam's Razor, the principle that you shouldn't make up entities unless
you have to. By this view, we are required to deny mental events in animals
whenever we can, in the name of parsimony.

All this sounds reasonable, but there's a fundamental flaw in it. Because we
have mental events, we already know that there are such things in the
universe. Denying them to animals therefore doesn't save anything; we
have the same number of entities on our hands no matter what we decide about
animal minds. So Occam's Razor doesn't provide any support for Morgan's Canon.
In fact, some of the animal rights philosophers claim that Occam's Razor is on their
side. They argue that if we're going to invoke intentions, desires, beliefs, and
other mental phenomena in accounting for our own actions, we should explain
other animals' behavior in similar terms whenever we can--again, in the name of
parsimony.

The problem with Morgan's Canon comes into sharp focus if we transfer the
argument from the brain to the kidney. Consider this version:

In no case may we interpret an animal's urine as the outcome of humanlike
biochemical processes, if we can find any other way of explaining it.

If Morgan's Canon represents a safe assumption, so does this
one. But it's obvious that this version is ridiculous, and that physiologists
would think I was crazy if I insisted they adopt this rule to avoid the
temptations of anthroporenalism. Then why does Morgan's Canon seem so
much more plausible than this one? Are neurologists just more gullible than
urologists? Or is there something special about events in the brain that makes
them different from events in the kidneys?

Part of the answer is that we don't care about kidneys the way we care about
brains, because brain events are a source of human status and kidney events are
not. Our mental abilities are markers of the moral boundary between animals and
people. Because nonhuman animals lack some of those mental abilities, we regard
them as property, to be used for our ends in any way we choose--on the dinner
table, or in scientific experiments, or transformed into soap and shoes and
lampshades. The only moral constraint that we observe on our use of other
animals is an obligation not to make them suffer. And we acknowledge that
duty only because we believe that at least some of the animals are on our side
of the second big line we draw across the moral landscape--the boundary
between sentience and nonsentience, between things that are conscious and things
that aren't. So both of our major moral boundaries are defined by things that go
on in the brain.

Up to this point, I have been assuming that mental events are, or are
produced by, events in the brain. Scientists rarely question this assumption,
but philosophers question it a lot. Brain events, they point out, are objective
and public; mental events are subjective and private. This is the other crucial
difference between the brain and the kidneys--and the other source of
scientists' qualms about the question of animal consciousness.

The intrinsic subjectivity of consciousness makes scientists uneasy.
Being conscious is the same thing as having private experiences; and the
scientific method is fundamentally committed to the assumption that private
experiences don't count as evidence. Only publicly accessible and repeatable
experiences have that status. If somebody makes a claim that you can't check out
for yourself, you're not obliged to take it seriously. This makes science
constitutionally antiauthoritarian, which is good; but it also makes it
unreceptive to claims about consciousness and its contents. Most of the recent
literature on the subject of consciousness is not really about consciousness at
all, but about either neurology or behavior. These are public phenomena, and
scientists know how to deal with them. So they spend a lot of time trying to
convince themselves that studying these things is somehow the same thing as
studying consciousness--like the drunk in the story who lost his wallet in
Central Park, but went looking for it in Times Square because the light was
better there.

Artificial Intelligence versus Human Essence

The field of computer science called artificial intelligence grew out of
these assumptions. In 1950, the English computer theorist Alan Turing offered a
famous test for telling whether machines can think. He called it "the
imitation game." Suppose, he said, that we can write a program that will
exchange messages with you. If, after five minutes of sending messages back and
forth, you can't tell whether you've been chatting with a human being or a
computer, then the machine has a human mind--because that's what having a human
mind means: being able to carry on a human conversation. What other test could
there be? And Turing predicted that some of us would see such machines within
our lifetimes. "I believe," wrote Turing, "that in about fifty
years' time it will be possible to program computers, with a storage capacity of
about 109, to make them play the imitation game so well that an
average interrogator will not have more than a 70 percent chance of making the
right identification after five minutes of questioning."

It's exactly fifty years later now, and 109 equals around 128
megabytes. You can buy the supercomputer of Alan Turing's fondest dreams off the
shelf at Sears for the price of a beat-up used car. Far bigger machines can be
had at higher prices. But none of them has yet been programmed to play the
imitation game successfully. What went wrong?

I think what went wrong wasn't just Alan Turing but the whole Western
conception of what it means to be human. Our traditions encourage us to define
ourselves not by what we are, but by how we are different: to
think of the human essence not in terms of our properties, but in terms
of our peculiarities--the small subset of human traits that we don't
share with any other creatures. Many of these human peculiarities hinge on our
unique skill in manipulating symbols, and that also happens to be what
philosophers get paid for doing. It's not surprising, therefore, that
philosophers and professors from Plato on down to Noam Chomsky have told us that
juggling words and numbers is the defining excellence that makes people special,
and that animals that lack it are mere objects. Marcus Aurelius summed it up in
this maxim: "Use animals and other things and objects freely; but behave in
a social spirit toward human beings, because they can reason."

Many Western thinkers have gone further and insisted that because animals
can't talk, their mental lives are defective in big ways, or even nonexistent.
"Thinking," wrote Wittgenstein, "is essentially the activity of
operating with signs." That view of thinking naturally appeals to college
professors, who sometimes get so consumed by operating with signs that they
wander around their campuses talking to themselves and tripping over shrubs. And
since nonhuman animals aren't very good at operating with signs, many
professional types have been reluctant to grant that beasts can have mental
lives at all.

Because Western thinkers have always attached so much importance to juggling
symbols as a marker of human status, and so little importance to walking around
without tripping over things (which couldn't be very important, because a donkey
can do it just as well as a philosopher), it was inevitable that when we managed
to build a symbol-juggling engine--a machine that could beat us all at chess and
prove the four-color theorem--our philosophers would try to persuade us that it
was human. Once we taught it to play the imitation game, they assured us, it
would be just like one of us. But so far, it has proved impossible to program
such an engine to succeed at the imitation game. The reason is that, although a
computer has many of the symbol-manipulating abilities that we prize so highly,
it lacks the subtler and more mysterious skills that come with being a sentient
animal, inhabiting and experiencing the world in a living body.

Computer metaphors have come to dominate our thinking about brain processes
and mental events. They predispose us to believe that mental events are algorithmic--that
is, that they are produced by executing a programmatic list of logically
connected instructions--and that digital computers (which are algorithm
machines) will eventually become conscious if only we can run the right program
on the right kind of hardware with the proper stored data. But as the
philosopher John Searle has argued forcefully, there are good reasons for
thinking that conscious awareness isn't, and can't be, produced by running a
computer program.

A digital computer is essentially a grid of slots, each of which can be
either full or empty. We think of these as ones and zeroes. Some of these slots
are linked causally by rules of operation, which provide that when a certain
pattern shows up in some area, the contents of other slots are changed in
various ways, which may depend on the contents of yet other slots. In modern
computers, the ones and zeroes are represented by electrical charges in
semiconductors, but they could be represented by anything: holes punched in
cards, or beads on wires, or eggs in egg cartons. The medium doesn't matter:
what's important is the algorithm. All the operations that you do on a computer
could be done in exactly the same way by giving a team of people written
instructions for moving eggs around in a football field full of egg cartons,
though of course it would take longer. (By the way, a football field full of egg
cartons has about 1 megabyte of RAM.)

This fact poses problems for computational theories of the mind. If moving
electrical charges around in a certain pattern can produce subjective awareness
and bring a mind into existence, so can moving around a collection of eggs in
the same pattern; and if I knew how many eggs to use and what rules of operation
to use in moving them, I could make my egg collection think it was Elizabeth
Dole or the Wizard of Oz. I could get the same effects by making chalk marks on
a blackboard, or waving semaphore flags, or singing songs, or tap dancing. All
these processes can be computationally equivalent, with algorithms that
correspond in every detail; but none of them seems like a plausible way of
producing a subjective awareness. And since a digital computer is just another
way of instantiating an algorithm, it seems impossible for such a device to
become conscious. If we ever succeed in creating an artificial intelligence,
it's going to have to be something more than just an algorithm machine.

How Is Consciousness Produced?

If consciousness isn't algorithmic, then how is it produced? We don't know.
The machineries of consciousness are an almost perfect mystery. Neuroscientists
and computer scientists have produced a lot of useful and suggestive models of
how the brains of animals process sensory data and judge and discriminate among
stimuli. We know that such mechanisms exist in our own brains, and that we need
them to perceive the world. But although these perceptual mechanisms are necessary
for consciousness, they aren't sufficient, because we can perceive things
and respond to them without being aware of them.

The most spectacular example of this is sleepwalking. Many people--as many as
30 percent of all children and 7 percent of adults--sometimes get up and start
walking around during the deepest, most unconscious part of sleep. Typically,
sleepwalkers open their eyes, sit up in bed with a blank facial expression,
pluck aimlessly at the bedclothes, and then rise up and walk. They ignore
objects and people nearby, but they usually manage to get around without bumping
into things. They may do very complicated and distinctively human things--talk,
make phone calls, get into a car and drive off, or even play musical
instruments. If you try to wake them up, they struggle violently to get away
from you; and if you succeed in awakening them, they're totally confused and
have no recollection of what they were doing or how they got there.

The phenomenon of sleepwalking shows that you can get surprisingly
complicated and even distinctively human behavior without consciousness. This
makes it much harder for us to find out anything about animal awareness. How do
we know that animals aren't simply sleepwalking all the time, even when they
appear to be awake? Do wolves hunt and horses gallop in their sleep, in the same
way that a human somnambulist gets into a car and drives off on the freeway at
65 miles an hour? When the cock crows in the morning, is the farmer the only
animal on the farm that wakes up? And if we can do so many things without being
conscious, then why did consciousness evolve?

Some people have argued that consciousness confers no adaptive advantage
whatever; it's just an incidental side effect of the neural events that produce
behavior. But I think that idea can be rejected for Darwinian reasons. If
consciousness were a useless epiphenomenon, natural selection would have
operated to get rid of it somehow, since we apparently have to pay a high price
to maintain it.

The price we pay for consciousness is unconsciousness, of the special kind we
call sleep. Most animals don't sleep. Invertebrates and cold-blooded vertebrates
usually have daily periods of torpor when they hide and rest, but most of them
show little or no correlated change in neural activity. Among vertebrates, true
sleep, involving a shift from fast to slow waves in the forebrain, appears to be
limited to mammals and birds, though there are hints of it in some reptiles.

Mammalian sleep is so dangerous, complicated, and time-consuming a
performance that we feel sure it must have a payoff of some sort, but it's not
really clear exactly what it is. On the face of it, it sounds like a bad idea to
spend about a third of the day plunged into a limp, helpless trance state that
leaves you unable to detect or react to danger. Some argue that sleep serves to
conserve energy, which is why we see it only in warm-blooded animals. The
trouble with this theory is that mammalian sleep uses almost as much energy as
wakeful resting. During eight hours of sleep, a human being saves only about 120
calories. These savings don't seem worth spending a third of your life dead to
the world. Another theory holds that sleep is a defense against predators; it's
nature's way of telling us to hide during those times of day when we don't need
to be active. The main problem with this story is that birds and mammals that
are too big to hide still have to flop down and fall asleep every day, right out
there on the prairie, exposed to every predator in the world. They do it as
little as possible--a horse sleeps only about 3 hours a day, of which only 20
minutes is spent lying down--but they'd be better off if they didn't do it at
all. They do it because they have to do it, not to save energy or avoid
predators.

Sleep appears to be something imposed upon us, not by our environmental
circumstances, but by the needs of the brain itself. Consciousness damages or
depletes something in the waking brain, and we can't keep it up indefinitely. If
we're forced to stay conscious around the clock, day after day, with rest but no
sleep, we soon start manifesting pathological symptoms, beginning with
irritability and proceeding through fainting and hallucinations to metabolic
collapse and death.

If sleep serves to restore something that is damaged or depleted by things
that go on when we are conscious, it seems reasonable to think that animals that
have to sleep as we do are conscious when they are awake. It seems significant
in this connection that animals that are (probably) never conscious don't sleep,
whereas sleep is compulsory for the animals that we know are sometimes conscious
(that is, people) and for those nonhuman animals that we suspect for behavioral
reasons may have mental lives something like ours. The natural inference is that
the waking state in these animals is also something like ours, that it includes
mental events and awareness of the world, and that the subjective differences
for them between being asleep and being awake parallel our own as closely as the
objective (neurological and behavioral) differences do.

The Evidence for Consciousness

Because we can't directly observe the contents of animal minds, the evidence
for animal consciousness is necessarily indirect. But it seems at least as
persuasive as the indirect evidence that we have for other unobservable
phenomena--for example, the Big Bang, or neutrinos, or human evolution. The
philosophers and scientists who refuse to acknowledge that dogs feel pain when
you kick them seem to me to suffer from the same kind of ingeniously willful
ignorance that we see in creationists who reject the notion of evolution because
they have never seen a fish turn into a chicken. I am inclined to believe that
these philosophers and scientists are not so much concerned about understanding
the universe as they are about looking tough-minded and spurning the temptations
of anthropomorphism.

To most of us, the temptations of anthropomorphism don't look quite so
dangerous as all that. Our close animal relatives, after all, are anthropomorphic
in the literal sense of the word, which means "human-shaped." They
have organs like ours, placed in the same relative positions. And interestingly
enough, they seem to recognize the same correspondences we do. Despite the
conspicuous differences in sight, feel, and smell between a human body and a
dog's, a friendly dog will greet you by licking your face and sniffing your
crotch, and a murderously angry dog will go for your throat--just as they would
behave in similar moods toward members of their own species. These are
sophisticated homology judgments; and they encompass not only anatomy, but
behavior as well. Just as we anthropomorphize dogs, horses, and other animals,
they cynomorphize and hippomorphize us--and each other--right back in the other
direction.

Psychological accounts of these facts often treat them as mistakes: category
errors, resulting from what the ethologist Heini Hediger called the
"assimilation tendency" in social animals. I suggest that the
assimilation tendency isn't a mistake, but an accurate perception of the way
things are. In a world inhabited by closely related species, it confers an
adaptive advantage. A gazelle that can tell when a lioness is thinking about
hunting is less likely to be eaten; a lioness that can tell when a gazelle is
thinking about bolting is less likely to go hungry. A man who doesn't notice
that a horse is furiously angry, or a horse that can't make that sort of
judgment about a human being, is correspondingly less likely to have offspring.
Insofar as anthropomorphism recognizes and incorporates these facts about the
world, it is not a vice but a survival skill. Indeed, one of the adaptive
advantages of consciousness itself may lie precisely in the fact that it
facilitates the reciprocal perception of other minds--not just in our own
species, but in others as well--by analogy with our own. If this perception is
adaptive, as I believe that it is, then perhaps we should stop resisting its
incorporation into the world view and vocabulary of science.